The long-term objective of this project is the development of improved non-isotopic homogenous immunoassays. Initially, a method will be developed whereby sulfhydryl groups will be transferred from an antigen to an antibody selectively near the latter's antigen binding site. Various fluorescence or enzyme probes can then be attached to the antibody at these sites. In view of their proximity to the antigen binding site, one can expect these probes to respond directly to antigen binding. Antibodies so labeled are therefore ideal for homogenous immunoassays in which the addition of a test sample containing the antigenic analyte will elicit an immediate measurable response, such as changes in fluorescence intensity or enzyme activity. Such immunoassays possess improvements over existing assay procedures with respect to sensitivity as well as reductions in cost, time and labor. Immunoassays are already used extensively for diagnostic tests in medicine. Yet untapped are markets in agriculture, environmental protection, pharmaceuticals, and other industries that require microanalyses of chemical substances. Immunoassay diagnostics kits are already manufactured by a number of companies. Technologies developd in this research will provide further impetus to existing industries, as well as spawn new industries in the production of immunoassay reagents and instruments.